Effect of Physicochemical Parameters on Sorption of Graphene Oxide Nanoparticles in Porous Media

Graphene Oxide (GO) is a two-dimensional carbon nanomaterial that has witnessed rapid increase in industrial production in the last decade and is likely to reach the subsurface through disposal of e-waste. Recent laboratory studies have also suggested that GO nanoparticles (GONPs) may also be used for insitu remediation of groundwater contaminated with toxic organic compounds and with the increasing GO production GONPs are expected to reach subsurface formations. The objective of this study is to understand the adsorption of graphene oxide nanoparticles (GONPs) onto quartz sand in pH range of 5.5 to 9 at 25 °C. Effects of natural organic matter in the form of Humic acid (HA) and Fulvic acid (FA) were also studied. Batch sorption experiments were conducted under varying concentrations of GO and quartz sand. Amongst several elutant studied for desorption and recovery of adsorbed GONPs from the quartz sand, deionized water was the most effective. The equilibrium attachment of GONPs onto quartz sand was analyzed using Linear, Langmuir, Freundlich, and Temkin adsorption isotherm models. Based on the Bayesian Information Criterion (BIC), the Langmuir isotherm provided the best fit to the adsorption data in the presence and absence of organic matter. The experimental results suggested that adsorption of GONP is affected by pH and presence of organic content. The highest adsorption capacity of 0.175 mg/g was observed at pH 6, while the lowest adsorption capacity of 0.0256 mg/g was recorded at pH 9. The maximum adsorption capacity of GO onto quartz sand at pH 8 showed no variation in the presence of FA or HA at a concentration of 12 mg/L. However, at higher concentrations of FA and HA, the adsorption of GONPs onto quartz sand increased in the presence of Humic Acid (HA) but decreased in the presence of Fulvic Acid (FA). Therefore, the remediation strategies need to consider the effects of pH and organic matter on the transport of GONPs in the subsurface. Significant desorption with the deionized water also suggests potential for mobilization of the adsorbed GONPs to the aquifer.